The present invention relates to iron compounds for use in medicine, notably in the treatment and prevention of iron deficiency anaemia and to methods of making such compounds.
An adequate supply of iron to the body is an essential requirement for tissue growth in both man and animals. Although there is normally an ample amount of iron in the diet, the level of absorption of iron from food is generally low so that the supply of iron to the body can easily become critical under a variety of conditions. Iron deficiency anaemia is commonly encountered in pregnancy and may also present a problem in the newly born. Moreover, in certain pathological conditions where there is blood loss, or where there is a mal distribution of iron in the body, there may be a state of chronic anaemia. This is seen in diseases such as Crohn""s disease, rheumatoid arthritis, certain haemolytic diseases and cancer.
Iron in the ferrous state (FeII) is a strong reducing agent and can also interact with and damage proteins carbohydrates and lipids and therefore be harmful to the body. Therefore iron is best delivered to the body and kept in the body in the ferric state (FeIII). However, it is difficult to do this because its solubility, and therefore its bioabsorption, is poor. The absorption rate of ferrous salts such as ferrous sulphate is typically 30% when given on an empty stomach but this causes unpleasant side effects particularly with chronic medication. When given with food, the absorption may fall to 1 to 3% of the administered dose. For some anaemias a daily uptake of 30 milligrams of iron is required, and although a wide range of iron compounds is already marketed for the treatment of iron deficiency anaemia, the poor levels of iron uptake by the body from these compounds necessitate relatively high dosage levels. However, the administration of high doses of poorly absorbed iron complexes may cause siderosis of the gut wall, and a variety of side effects such as stomach pains, nausea, vomiting, constipation and heavy black stools which can result in poor patient compliance with their treatment.
GB 2128998 and EP 0159194 describe neutral ferric iron complexes of various 3-hydroxy-4-pyrones in an iron:hydroxypyrone molar ratio of 1:3. The complexes are described for use at relatively low dosage levels for ferric compounds in the treatment of iron deficiency anaemia. In the body, these complexes were considered to be transferred into the gastrointestinal cell and then dissociate to provide iron for absorption and transfer on to the body""s natural uptake processes. However, the complexes of iron described in the above documents suffer from the significant problem that if dissociation of the complex occurs in an unfavourable environment in the body, particularly the gastrointestinal tract, native iron can be formed which precipitates and is therefore not absorbed.
GB 2128998 teaches that only a neutral complex comprising maltol and iron in the ferric state in a molar ratio of 3:1 (maltol:iron) confers a therapeutic effect. By contrast, charged complexes having maltol:iron molar ratios of 1:1 or 2:1 are shown by in vitro tests to be unsatisfactory so that iron from these complexes would not be expected to be taken up to a satisfactory extent in vivo, making them unsuitable for use in medicine.
It is an object of the invention to provide iron complexes for use in medicine, notably in the treatment of iron-deficiency anaemias, which complexes do not suffer from, or substantially mitigate, the above and other problems of known complexes.
It is also an object of the invention to provide methods for making iron complexes and pharmaceutical compositions.
According to a first aspect, the invention provides an iron complex comprising iron in the ferric state and a hydroxypyrone ligand; charcterised in that the iron and hydroxypyrone ligand are provided in combination with a carboxylic acid, most preferably a hydroxycarboxylic acid as a counter ion.
Preferably the carboxylic acid is a C1 to C6 acid, particularly those having from 1 to 3 carboxylic groups.
Preferably the acid is selected from one or more of citric acid, isocitric acid, gluconic acid, succinic acid, fumaric acid and tartaric acid. Conveniently, it is the tri-basic acid, citric acid and is present in a formulation in an amount sufficient to generate a concentration in solution in the blood of from 0.1 to 100 mM following administration, preferably in an amount of 10 to 1000 mg per dose.
It should be appreciated that carboxylic acids such as citric acid, being iron chelators, would have been expected to form mixed ligand complexes with the iron chelates of the aforesaid hydroxypyrones, but these complexes would have been charged. Surprisingly, when citric acid was added to iron complexes of 3-hydroxy-4-pyrones no mixed ligand complexes were identified, but in solution the citric acid behaves as a counter ion (anion) to the iron/hydroxypyrone complex, helping to maintain more iron in solution and available for absorption.
Unlike the neutral chelated mixed ligand complexes mentioned in GB 2 157 686 A (National Research Development Corporation), in which there is an internal balance of charges between the ferric cation and the ligands bound covalently thereto (see page 1, lines 45 to 48), it will be appreciated that the carboxylic acid acts as a counter ion (non-covalently bound anion) in the complexes of the invention.
Certain aspects of the carboxylic acid containing compositions of the first aspect of the invention may enhance the activity of the iron complexes in particular contexts. Thus, although the neutral ferric complexes containing a 1:3 molar proportion of iron:hydroxypyrone are of particular value as being stable over a wide pH range from about 4 to 5 up to 10, if administered orally, they will dissociate at the pH values of less than 4 prevailing in the stomach to form a mixture of the 1:2 and 1:1 complex together with free ligand. Unexpectedly, the presence of carboxylic acid enhances the solubility of these intermediate complexes rather than the formation of mixed ligand complexes and any excess iron generated is trapped as carboxylated iron rather than being precipitated as insoluble hydrated iron forms which are not available for bioabsorption. This effect is entirely unexpected because a carboxylic acid such as citrate on its own is very poor in enhancing iron transport across cell membranes. Advantageously, the presence of a carboxylic acid such as a citrate also maintains solubility at the wide pH range found in the upper intestinal tract.
The pH of the stomach can vary before and after meals and can also be dependent on other medications, such as antacids. The enhanced solubility provided by the compositions of the invention provides a more regular and reproducible supply of iron on a day to day basis than known compositions.
In a further aspect, the invention provides a method of preparing the iron complexes according to the first aspect of the invention comprising reacting ferric iron with at least one hydroxypyrone and combining the resultant complex with a carboxylic acid, preferably citric acid.
The iron hydroxypyrone complexes of the invention can be prepared by dissolving iron (III) carboxylate, especially citrate, in unbuffered water at a concentration of from 0.1 to 1M. A quantity of hydroxypyrone dissolved in a solvent is added to the solution in the desired 1:1:1 iron:hydroxypyrone:carboxylic acid molar proportion with rapid stirring. This ensures that the reaction is non-covalent, ie. the carboxylic acid acts as a counterion. In the preferred method using 1:1 molar proportions of iron citrate to ethylmaltol dissolved in ethanol, a deep red coloured solution of [FeIII ethylmaltol]2+ citrate2xe2x88x92 is formed. After stirring for 15 mins, the ethanol is removed by evaporation at atmospheric pressure. The resulting solution is freeze dried to yield a deep red powder.
Alternatively, iron complexes are prepared in accordance with the methods described in example 1 of GB 2128998 and EP 0159914, by the reaction of a mixture of compounds which provide the ligands and iron ions, the latter conveniently being derived from an iron salt, particularly a ferric halide and especially ferric chloride. A carboxylic acid such as citrate is then added to the resultant iron complexes to form complexes of the first aspect of the invention with the carboxylic acid as a counter ion. It will be appreciated that the relative amounts of the components are selected to produce a 1:1:1 molar ratio complex of iron:hydroxypyrone:carboxylic acid.
To obtain a preferred liquid preparation of the complexes of the first aspect of the invention a solution of iron (FeIII) is reacted with hydroxypyrone and a carboxylic acid, preferably the tri-basic acid citrate, is added until a precipitate of the 1:3 iron/hydroxypyrone molar ratio complex forms. The precipitate is removed and the supernatant comprises a liquid preparation of a mixture of the 1:1 and 1:2 iron hydroxypyrone complexes with citrate as an anion.
Preferably, the iron concentration is from 0.01M to 1M and the solution is buffered to a pH of from 3.0 to 7.0. Preferably, the hydroxypyrone is maltol or ethylmaltol.
It will be appreciated that the iron/hydroxypyrone complexes with a carboxylic acid such as citrate according to the first aspect of the invention can also be formed in vivo by administering the iron/hydroxypyrone complex and the carboxylic acid sequentially rather than simultaneously. In vivo, the acid can act as a counter ion to enhance the solubility of the iron. Such a method of manufacture is intended to fall within the scope of the first aspect of the invention.
The invention also relates to the use of an iron complex as defined above for the first aspect of the invention, in the manufacture of a composition for use in medicine.
The invention also relates to the use of an iron complex according to the first aspect of the invention in the manufacture of a composition for use in animals as well as for human use Preferably the medical use is in the treatment or prevention of iron deficiency anaemia.
Preferably, the hydroxypyrone is a hydroxy-4-pyrone, and expecially a 3-hydroxy-4-pyrone or a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms, or a 5-hydroxypyrone, such as Kojic acid.
The substituted 3-hydroxy-4-pyrones may carry more than one type of aliphatic hydrocarbon group but this is not usual and substitution by one rather than two or three aliphatic hydrocarbon groups is preferred. The term aliphatic hydrocarbon group is used herein to include both acyclic and cyclic groups which may be unsaturated or saturated, the acyclic groups having a branched chain or especially a straight chain. Groups of from 1 to 4 carbon atoms and particularly of 1 to 3 carbon atoms are of most interest. Saturated aliphatic hydrocarbon groups are preferred, these being either cyclic groups such as the cycloalkyl groups cyclopropyl and especially cyclohexyl or, more particularly, acyclic groups such as the alkyl groups n-propyl and isopropyl, and especially ethyl and methyl. Substitution at the 2- or 6-position is of especial interest although, when the ring is substituted by the larger aliphatic hydrocarbon groups, there may be an advantage in avoiding substitution on a carbon atom alpha to the 
system. This system is involved in the complexing with iron and the close proximity of one of the larger aliphatic hydrocarbon groups may lead to steric effects which inhibit complex formation Examples of specific compounds whose iron complexes are of use in the present invention are shown by the following formulae (I), (II) and (III): 
in which R is a cycloalkyl or alkyl group, for example methyl, ethyl, n-propyl or isopropyl Among these compounds 3-hydroxy-2-methyl-4-pyrone (maltol; II, R=CH3) is of most interest, whilst 3-hydroxy-4-pyrone (pyromeconic acid; I), 3-hydroxy-6-methyl-4-pyrone (III, R=CH3) and particularly 2ethyl-3-hydroxy-4-pyrone (ethylpyromeconic acid; II, R=C2H5) are also of especial interest. For convenience the compound 3-hydroxy-2-methyl-4-pyrone is referred to herein as xe2x80x9cmaltolxe2x80x9d.
Certain hydroxypyrones, such as maltol, are available commercially. With others, a convenient starting material in many instances consists of 3-hydroxy-4-pyrone which is readily obtainable by the decarboxylation of 2,6dicarboxy-3-hydroxy-4-pyrone (meconic acid). For example, 3-hydroxy-4-pyrone may be reacted with an aldehyde to insert a 1-hydroxyalkyl group at the 2-position, which group may then be reduced to produce a 2-allyl-3-hydroxy-4-pyrone. The preparation of 2ethyl-3-hydroxy-4-pyrone, etc, by this route is described in U.S. application Ser. No. 310,141 (series of 1960) now abandoned. Other preparation methods are described by Spielman, Freifelder, J. Am. Chem. Soc. Vol 69 Page 2908 (1947).
It will be appreciated by skilled persons that these are not the only routes available to these compounds and their iron complexes and that various alternatives may be used.
Advantageously, the iron ion is provided in combination with 3-hydroxy-4-hydroxypyrone as a 1:3, 1:2 or 1:1 iron:hydroxypyrone molar ratio complex.
In a second aspect the invention provides a method of making a composition comprising mixing a ferric iron compound, other than an inorganic ferric salt, and a hydroxypyrone wherein the iron compound and hydroxypyrone are mixed in the dry state. Preferably the compositions obtained is for use in medicine.
By xe2x80x9cin the dry statexe2x80x9d we include the meaning that the components are provided in a form substantially free from water. Preferably, the components are in the form of a powder.
By xe2x80x9cinorganic saltxe2x80x9d we include ferric nitrate, ferric sulphate and ferric halides such as ferric chloride. Preferably, the ferric iron compound comprises a carboxylic acid such as citrate, advantageously ammonium citrate, or tartrate. The carboxylic acid can also be added separately to the mixture either on its own or preferably as a complex with iron. The carboxylic acid appears to promote the formation of ferric monohydroxypyrone species ie. a 1:1 (iron:hydroxypyrone) molar ratio complex in aqueous solution or in vivo.
The carboxylic acid component of the mixture may be present in excess. Preferably, the method further comprises adding a pharmaceutically acceptable diluent or carrier to the mixture simultaneously or subsequently.
Using the above xe2x80x9cdry mixxe2x80x9d method of the invention one can easily vary the relative proportions of the components to produce any molar ratio of iron to hydroxypyrone that is required. In particular, the method provides a simple way of making compositions in which the molar ratio of iron to hydroxypyrone is less than 1:3, especially 1:2 and 1:1.
In a preferred embodiment the components of the mixture are ferric carboxylate and a ferric hydroxypyrone complex in a 1:3 iron:hydroxypyrone molar ratio. The components are preferably provided in relative amounts whereby the molar ratio of iron:hydroxypyrone:carboxylic acid in the resulting mixture is 1:1:1.
The inventors have shown that in aqueous solution such a mixture produces ferric monohydroxypyrone species which exhibit a much higher solubility than the individual components of the mixture For example, ferric citrate and ferric trimaltol have a respective solubility of less than 10 mg/ml at pH 7.0. When used in the dry mix method of the preferred embodiment however, the 1:1:1 molar ratio (iron:maltol:citrate) mixture produced exhibits a solubility of more than 100 mg/ml, that is, more than then times greater than that of ferric citrate or ferric trimaltol. This synergistic effect is entirely unexpected.
It appears that, in aqueous solution, the mixture rearranges to form highly soluble iron chelates comprising the 1:1 iron:maltol molar ratio complex with up to approximately 25% of the 1:2 iron:maltol complex, depending on the ratio of ferric citrate to ferric trimaltol used in the dry mix method. The carboxylic acid (eg, citrate) appears to act as a counterion across the pH range, although there may be some partial chelation. The inventors have also found that the compositions produced by the above dry mix method are stable over a wide pH range
The dry mix method according to the second aspect of the invention also provides a most convenient method of making a complex according to third and fourth aspects of the invention.
The third aspect of the invention provides an iron complex which comprises iron in the ferric state and a hydroxypyrone; characterised in that the complex is substantially free from complexes having iron:hydroxypyrone in a molar ratio of 1:3 and is for use in medicine.
Although the term xe2x80x9csubstantially free fromxe2x80x9d will be understood readily by a skilled person, it includes the meaning that the complex includes not more than 15% and preferably less than 15% by weight of the 1:3 iron:hydroxypyrone molar ratio complex based on the total weight of the complex.
Preferably, the complex comprises a 1:1 molar ratio of iron:hydroxypyrone containing not more than 25% and conveniently less than 15% by weight of iron:hydroxypyrone complex in a molar ratio of 1:2.
Advantageously, the complex has a total molar ratio of iron:hydroxypyrone of from 1:1 to 1:2, preferably 1:1.5 to prevent formation of the 1:3 molar ratio complex.
In a fourth aspect the invention provides a solid pharmaceutical composition comprising a complex of iron in the ferric state and a hydroxypyrone, which composition is substantially free from complexes having iron:hydroxypyrone in a molar ratio of 1:3 and further comprises an uncomplexed hydroxypyrone.
The present inventors have discovered that, contrary to their expectations in view of GB 2128998, iron:hydroxypyrone complexes having molar ratios of 1:1 or 1:2 (iron:hydroxypyrone), especially 1:1, are well taken up in vivo, making them suitable for increasing the level of iron in a patient""s bloodstream.
The complexes according to the third and fourth aspects of the invention are surprisingly stable for extended periods (eg. six months) over a wide pH range. This is advantageous because the quantity of hydroxypyrone, and therefore the cost of manufacture, is reduced compared to known neutral. 1:3.iron:maltol compositions. In addition, a reduced quantity of hydroxypyrone enables preparations to be made which contain less than the World Health Organisation (WHO) recommend acceptable daily intake (ADI) for such hydroxypyrones. This makes the preparations of the invention suitable for nutritional/over the counter (OTC) usage.
Solutions of the complexes of the invention display unexpected stability even at high concentrations and at high acidic to neutral pH values. For example, although the natural pH of ferric monomaltol is approximately 2.8 it displays stability for extended periods (for example six months) at a buffered pH of 7. This is unexpected because all other soluble forms of ferrous iron such as FeSO4 precipitate very rapidly at pH 7.
The complexes of the invention can therefore be used in the manufacture of liquid formulations for use in medicine. As the liquid formulation can be buffered to a physiologically acceptable pH value, that is a pH value such as neutral pH 7 at which irritation on administration is absent or at a satisfactory level, the liquid formulations are suitable for intravenous or intramuscular injection. They are also less irritant than acidic solutions when administered orally since acidic solutions can cause irritation, particularly in the duodenum.
It will be appreciated that a variety of known buffering agents can be employed to buffer the pH of the liquid formulations of the invention around neutral to make them particularly suitable for administration by injection. Examples of suitable buffering agents include bicarbonates, sodium acetate, amino acids such as lysine and various non-chelating weak carboxylic acids.
It will be appreciated that known neutral 1:3 ferric iron:3-hydroxy-4-pyrone molar ratio complexes are unsuitable for formulation as a liquid due to their poor solubility (approximately 4 mg /ml). One would need to drink an unacceptably large volume of such liquid formulations to get sufficient iron uptake.
Iron sorbitol (eg. Jectofer(trademark)xe2x88x9250 mg/ml ferrous iron in 2 ml ampoules, sold by Astra UK) is known for intramuscular injection in the treatment of iron-deficiency anaemia where oral administration is ineffective, but it is not suitable for intravenous injection.
Initial toxicity studies by the inventors have shown that liquid formulations of the complexes of the invention, such as iron monomaltol, do not cause red blood cell haemolysis and red blood cell breakdown, making them suitable for injection. This is in contrast to the published results of Rice-Evans and Baysal (J. Biochem 1987 244, 191-196), which demonstrated that iron salts damage red blood cells and are too toxic for injection.
The inventors have also shown that the liquid formulations of complexes of the invention induce when incubated with hemoglobin (Hb) induce relatively little (less than 5% in 2xc2xd hours) methaemoglobin (met-Hb) formation. It would be undesirable to form met-Hb, a stable oxidation product of Hb in the blood with an injectable formulation. Met-Hb formation has been suggested as an indicator of free radical damage and therefore toxicity.
The effectiveness of iron uptake using solutions of the complexes of the invention is very surprising in view of the conclusions of Seeberg et al [(Science (1954) 119, 608-609)] who injected chelated iron (ferric sodium ethylenediamine tetraacetate-FeEDTA) into rats intravenously and observed extremely poor iron uptake. They concluded that metal ions injected intravenously remain attached to the nucleus of the complex and are not readily available to the uptake systems in the body.
The inventors have shown rapid donation of iron from the complexes of the invention to the body""s iron uptake molecule, the protein transferrin. This was demonstrated by incubating apotransferrin (ie. transferrin not bound to iron) with a solution of a complex of the invention. The colour of the solution disappears rapidly, indicating donation of iron to apotransferrin.
Particularly preferred complexes of the invention comprise the 1:1 complexes of iron maltol and iron ethyl maltol. These complexes have been found to be approximately ten times more soluble than the 1:3 iron/hydroxypyrone molar ratio complex.
The advantage of a 1:1 iron/hydroxypyrone molar ratio complex for pharmaceutical purposes is that it contains a equimolar ratio of iron:hydroxypyrone. For example, ethylmaltol can be administered to the general public at a dose of 2 mg kgxe2x88x921 of body weight 24 hxe2x88x921 for life. Thus for a 50 kg person, a daily dose of 100 mg of ethylmaltol is permitted. In a complex of the invention, 100 mg of ethylmaltol can be associated with 40 mg of ironxe2x80x94a suitable dose for an over-the-counter (OTC) product. Additionally, the 1:1 iron/hydroxypyrone complexes are preferred because they use less hydroxypyrone, leading to cost savings and a reduction in toxicity concerns due to the hydroxypyrone per se.
Other preferred iron complexes are described in GB 2128998 and EP 0159194, the disclosures of which are incorporated herein. A feature of the iron complexes disclosed in these documents is that the complexes were designed to be of neutral charge, ie. there is an internal balance of charges between the ferric cation and the ligands bound covalently thereto, there being no need for any additional non-covalently bound anions, such as chloride, to balance the charge on the ferric cation.
In a fifth aspect the invention provides a method of making a composition for use in medicine comprising mixing a hydrated ferric salt with a hydroxypyrone to form a 1:1 molar ratio (iron:hydroxypyrone) complex. The resulting solution has a ferric monohydroxypyrone concentration of approximately 10 molar. Preferably, a caxboxylic acid is added to the mixture simultaneously or subsequently. Preferably the method further comprises adding a pharmaceutically acceptable carrier to the mixture, either simultaneously or subsequently. The mixture may then be dried.
The hydrated ferric salt may comprise a counter ion such as a carboxylic acid, preferably citrate, or ammonium citrate; or a halide, preferably chloride, or nitrate.
Particularly preferred hydrated ferric salts include ferric chloride hexahydrate (CAS No. 10025-77-1) and the brown hydrated form of ferric ammonium citrate (CAS No. 1332-98-5) or the green hydrated form (CAS No. 1333-002) which contain 16.5-18.5% and 14.5-16% of iron and 65% and 75% of citric acid respectively.
Preferably the hydrated ferric salt and hydroxypyrone and, optionally the carboxylic acid, are provided as powders and are mixed by trituration.
It will be appreciated that the above method is particularly suitable for making complexes and compositions according to the first, third and forth aspects of the invention. Further, the invention provides compositions for use in medicine comprising mixtures obtainable by the methods of the fourth aspect of the invention.
In a further aspect the invention relates to a pharmaceutical composition comprising an iron complex of the invention together with a pharmaceutically acceptable diluent or carrier.
By xe2x80x9cpharmaceutically acceptablexe2x80x9d we include the normal meaning that the carriers must be xe2x80x9cacceptablexe2x80x9d in the sense of being compatible with the active ingredient (complex) and not deleterious to the recipients thereof
The composition may be in the form of a solid or liquid. Suitable solid carriers include starch, lactose, dextrin and magnesium stearate. Liquid carriers should be sterile and pyrogen free: examples are saline and water.
The complexes of the invention provide particular advantages in relation to the formulation of iron complexes. Liquid formulations of the iron complexes are particularly suitable for oral and parenteral administration. In such applications, the solubility of some known iron complexes is unsatisfactory.
The iron complexes may be formulated with a physiologically acceptable diluent or carrier for use as pharmaceuticals for veterinary or human use in a variety of ways. However, compositions in which the diluent or carrier is other than a non-sterile solution in water and/or an organic solvent are generally preferred. Thus, the iron complexes may be applied as an aqueous, oily or emulsified composition incorporating a liquid diluent, which will, however, most usually be employed for parenteral administration and therefore may conveniently be sterile and pyrogen free. One form of composition of particular interest thus has the form of a sterile, injectable solution. Oral administration is, however, more generally to be preferred for the treatment or iron deficiency anaemia in humans and the complexes of the present invention may be given by such a route.
Oral administration is often preferred for the treatment of iron deficiency anaemia in humans and the compositions of the present invention may be given by that route. For oral administration in humans, it is more usual, to use compositions incorporating a solid carrier, for example starch, lactose, dextrin or magnesium stearate. Such solid compositions may conveniently be shaped, for example in the form of tablets, capsules (including spansules), etc. However, liquid preparations are especially useful for oral administration to patients who have difficulty in swallowing solid forms. Such difficulties are common in patients suffering from anaemias associated with arthritis.
Other forms of administration than by injection or through the oral route may also be considered, for example the use of suppositories.
More than one iron complex of the invention may be contained in a pharmaceutical composition, and other active compounds may also be included. Typical additives include compounds having the ability to facilitate the treatment of anaemia, such as folic acid. A zinc source may also be included.
Iron compounds used in the treatment of iron deficiency anaemia can inhibit the mechanism of zinc uptake in the body. This can cause serious side effects in the foetus when pregnant females are treated for anaemia. The iron complexes of the present invention are advantageous in that they either do not exhibit this effect at all, or exhibit the effect at lower levels than known compounds for the treatment of anaemia. Accordingly, only small quantities of a zinc source, if any, are required.
The compositions are particularly useful for milder anaemias where a lower daily dose of iron enables better compliance with treatment. Other approaches may involve various types of controlled release system, providing a delayed release of the complex with time, or a system which is resistant to dissociation under acidic conditions, for example by the use of buffering, or a system which is biased towards release under conditions found in the small intestine. This may be a pH sensitive system which is stabilised towards a pH of 1 to 3 typical of the stomach but not one of 7 to 9 typical of the small intestine. Since the pH of the stomach is higher after a meal, it may be advantageous, whatever method or formulation is used, to administer the iron complexes at such a time.
The present invention includes a method for the treatment of a patient to effect an increase in the levels of iron in the patient""s bloodstream which comprises administering to said patient an effective amount of an iron complex as defined previously.
In addition to the pharmaceutical uses, the iron complexes also have utility as a source of iron in various other applications including animal, bacterial and plant cell growth media, or in colouring agents, and also in the control of iron transport across membranes.
The iron complexes of the invention can be prepared by the reaction of the hydroxypyrone and iron ions, the latter conveniently being derived from an iron salt, particularly a ferric halide and especially ferric chloride. The reaction is conveniently effected in a suitable mutual solvent and water may often be used for this purpose. If desired, however, an aqueous/organic solvent mixture may be used or an organic solvent, for example ethanol, methanol, acetone, or chloroform and mixtures of these solvents together and/or with water where appropriate. In particular, methanol or especially ethanol may be used where it is desired to effect the separation of at least a major part of a by-product, such as sodium chloride, by precipitation whilst the iron complex is retained in solution.
To prepare the 1:1 ferric:hydroxypyrone complex, the hydroxypyrone and the ferric salt are conveniently mixed in solution in an equal molar proportion and the pH adjusted to a value in the range of 1 to 2, preferably 1.
Reaction to form the iron complex is generally rapid and will usually have proceeded substantially to completion after 5 minutes at about 20xc2x0 C., although a longer reaction time may be used if necessary. Following separation of any precipitated by-product, such as sodium chloride in the case of certain solvent systems, the reaction mixture may conveniently be evaporated on a rotary evaporator or freeze dried to yield the solid iron complex. This may, if desired, by crystallised from a suitable solvent, for example water, an alcohol such as ethanol, or a solvent mixture, including mixtures containing an ether.
In a further aspect, the present invention provides a process for the preparation of a 1:1 hydroxypyrone:iron complex, preferably a 1:1 hydroxypyrone:iron(III) complex of 3-hydroxy-4-pyrone or of a 3-hydroxypyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms, which comprises reacting said hydroxypyrone with ferric ions at a pH in the range of 1 to 2 to form the 1:1 complex and isolating said complex in the solid form.
In a preferred method the iron salt (eg.. FeCl3) and hydroxypyrone are reacted in an organic solvent, such as ethanol, which can be evaporated readily to yield the 1:1 iron:hydroxypyrone molar ratio complex. The evaporated solvent may be recycled, if desired. The reaction mixture does not need to be adjusted to pH 1-2 in this method because it is naturally highly acidic.
Whilst for some uses it may be appropriate to prepare the iron complex in substantially pure form, ie. substantially free from by-products of manufacture, in other cases, for example with a solid oral formulation as described hereinafter, the presence of by-products such as sodium chloride may be quite acceptable.
In a further aspect, the present invention provides a pharmaceutical composition comprising a pharmaceutically effective amount of a 1:1 hydroxypyrone:iron (III) complex, preferably of an hydroxypyrone such as 3-hydroxy-4-pyrone or of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms, together with a physiologically acceptable diluent or carrier.
Compositions may be formulated in unit dosage form, ie. in the form of discrete portions containing a unit dose, or a multiple or sub-unit dose. Whilst the dosage of hydroxypyrone iron complex given will depend on various factors, including the particular compound which is employed in the composition, it may be stated by way of guidance that maintenance at a satisfactory level of the amount of iron present in the human body will often be achieved using a daily dosage, in terms of the iron content of the compound, which lies in a range from about 0.1 to 100 mg and often in a range from 0.5 to 10 mg, for example 1 or 2 mg, veterinary doses being on a similar g/kg body weight ratio. However, it will be appreciated that it may be appropriate under certain circumstances to give daily dosages either below or above these levels. In general, the aim should be to provide the amount of iron required by the patient without administering any undue excess and the properties of the pharmaceutical compositions according to the present invention are particularly suited to the achievement of this aim. Similarly, the concentration of iron in the pharmaceutical composition in the form of the hydroxypyrone complex may vary quite widely, for example over a range from 0.01 to 20% w/w. However, it is more usual for the concentration to exceed 0.01% w/w and it may often exceed 0.05 or 0.1% w/w, whilst a more usual limit for the upper end of the range is 13% w/w. A common range of concentration is 0.05 to 5% w/w, for example 0.2 to 0.5, 1 or 2% w/w.
The present invention further includes the use of an iron complex of the invention comprising a 3-hydroxy-4-pyrone or of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms, for the manufacture of a medicament for use in effecting an increase in the levels of iron in a patient""s blood stream
In a further aspect the invention provides a composition comprising a complex of the invention in admixture with an uncomplexed hydroxypyrone.
A small excess of uncomplexed hydroxypyrone is advantageous because it can chelate (form a complex with) any free iron in vivo, making the iron available for bioabsorption.
The molar proportion of the uncomplexed (free) hydroxypyrone to the iron complex should be selected so that the amount of chelated (complexed) iron available for bioabsorption is maximised in vivo and iron:hydroxypyrone complexes having a molar ratio of 1:3 are substantially not generated. A preferred range for the molar proportion of the free hydroxypyrone present in compositions according to the present invention is thus up to 1 mole of free hydroxypyrone:1 mole of iron hydroxypyrone complex. Conveniently, a proportion of up to no more than 0.25 moles:1 mole is used with a lower level of less than 0.25 moles:1 mole, especially less than 0.15 moles: 1 mole being preferred.
In a fifth aspect the present invention includes a mixture of a 1:1 hydroxypyrone:iron (III) complex, such as 3-hydroxy-4-pyrone or of a 3-hydroxy-4-pyrone in which one or more of the hydrogen atoms attached to ring carbon atoms are replaced by an aliphatic hydrocarbon group of 1 to 6 carbon atoms, together with a different such hydroxypyrone or a salt thereof containing a physiologically acceptable cation.
In a sixth aspect the invention provides a diet supplement comprising or consisting of one or more hydroxypyrones. Preferably the supplement is devoid of iron.
Preferably, the supplement is for simultaneous or sequential administration with a carboxylic acid, especially citric acid If desired, the carboxylic acid may be included in the supplement.
The inventors have demonstrated that the above diet supplement can be used to increase iron absorption in vivo It is believed that the hydroxypyrone combines with iron supplied in the diet to form the 1:1 iron:hydroxypyrone molar ratio complex of the invention
As mentioned previously, it was accepted wisdom in the art that effective iron absorption in vivo was due to the 1:3 iron:hydroxypyrone molar ratio complex. Such a technical prejudice would lead a skilled person away from the concept of using a hydroxypyrone such as maltol as a diet supplement because the amount of hydroxypyrone needed to form the 1:3 iron:hydroxypyrone molar ratio complex would exceed the WHO recommended ADI for hydroxypyrones such as maltol.
A normal balanced diet in man provides approximately 20 milligrams of iron per day. The hydroxypyrone diet supplement should contain enough hydroxypyrone to form the 1:1 iron:hydroxypyrone molar ratio complex in vivo. In the case of the hydroxypyrone maltol for example, the diet supplement should contain approximately 30 to 50, preferably about 40 milligrams of maltol per daily dose. In general, such an amount would not exceed the recommended ADI of 1 mg /kg body weight for maltol.
It will be appreciated that the amount of the hydroxypyrone in the diet supplement can be varied depending on the amount of iron provided by the recipients daily diet.
The diet supplement of the invention can be provided in solid or liquid form. Various known flavourings may be added to the hydroxypyrone diet supplement to improve its palatability.
In a further aspect the invention provides a hydroxypyrone such as maltol, for use in the manufacture of a diet supplement. Preferably the food supplement is for use in medicine, particularly for increasing the level of iron in a patient""s bloodstream in the treatment of iron-deficiency anaemias.